What may be the most brilliant single investigation in the history of experimental psychology

1 Psychological Laboratories for Experiments with Single Humans

Psychological laboratories are equipped for two purposes. Firstly, for the recording of behavior and for the monitoring of mental and emotional states; secondly, for the systematic control of environmental and individual factors which influence and determine human mental and emotional states. Experiments are designed to relate measures of behavior and internal states as dependent variables to preceding or concomitant environmental and individual factors as independent variables. Typically, these kinds of experiments are conducted with individuals. The data from these samples are then accumulated over successive experimental sessions.

As one class of dependent variables, behavioral data primarily comprise speed and quality of performance in achievement tasks. The achievements tested include learning (e.g., reproduction of texts), perception (e.g., estimating distances), problem solving (e.g., finding the shortest route in a labyrinth), and sensorimotor actions (e.g., reacting to a light signal). Besides assessing performance, behavioral records also serve as indications for habitual or transient mental and emotional states (e.g., fatigue, positive affect, and surprise). An example is observations of facial expressions indicating emotional reactions. Moreover, behavioral records reflect stable personality traits (e.g., self-efficacy, anxiety, and withdrawal).

Another class of dependent variables are self-reports. Self-reports of participants express judgments and mental processes (e.g., logical reasoning), mental structures (e.g., impressions of paintings), and emotional states (e.g., optimism). A third class of dependent variables is psycho- and neurophysiological data. Measures of the autonomic nervous system (e.g., cardiovascular and gastrointestinal activity) and the endocrine system (e.g., adrenaline and cortisol secretion) serve as evidence for stable and transient states. More directly related to cognitive and sensorimotor processes are cerebral functions (e.g., event-related brain potentials).

Several unobtrusive methods exist for collecting experimental data. These include free protocols, video and voice recordings. However, most methods are obtrusive, for instance performance tests, which entail the operation of technical devices (e.g., reaction keys for measuring the speed of manual reactions). The obtrusive methods include various kinds of psycho- and neurophysiological recordings where participants are placed in or connected with special appliances ranging from blood pressure meters to magnetic resonance tomographs.

The instructions and tasks provided for the participants are the crucial aspects of the independent variables. These tasks may be tests of memory and learning, or of cognitive and motor skills. They may initiate logical judgments and actions, and may arouse emotions. Instructions not only serve to explain the requirements of the experimental tasks, but are also designed to affect the participants' motivation, attitudes, and moods. A plethora of devices exists for various experimental designs such as the presentation of visual or acoustic stimuli and for the control of environmental variations, which permit to study learning, movement, communication, and self-regulation. The appliances should guarantee precise and stable conditions over repeated trials. They also enable the scientist to control the variations in experimental conditions, such as the time of exposure to visual stimuli as measured in milliseconds.

The establishment of psychological laboratories for humans benefited from growing expertise in pertinent experimental techniques and the feasibility of exact measurements. Many experimental investigations depended on the progress made in precision mechanics. In the early stages of experimental psychology, most research laboratories employed a mechanical engineer. The advent of electronic elements also revolutionized experimentation, and has brought electronic engineers into the psychological laboratories. Increasing demands and standardization requirements permitted the commercial production of the devices used in psychological research. Thereafter, more and more technical research instruments were purchased and maintained by commercial companies, and the technical work force within the research laboratories diminished. This process continued when laboratory computers became available which could be adapted to various experimental purposes by specialized software.

For many decades, most psychological laboratories for humans were part of the university departments of psychology. Most of them were rather small, consisted of a few rooms, and were located alongside offices and classrooms. Some were insulated for sound or light protection to permit better control over sensory stimulation. Some were electrically shielded to enable electrophysiological data collection. Laboratories in psychological departments were rarely set up as central, permanent research units. Neither were they equipped for a variety of research tasks. Most of them served a specialized form of research (e.g., perception psychology). They were maintained by individual researchers and small work groups, and were often transferred to other purposes once a project or a contract was terminated. However, psychology departments had a policy of employing at least one experimentalist in their staff who raised funds and organized a laboratory for scientific research and academic training.

As brain research gained in recognition, special institutions of neuroscience with a high emphasis on medical and biological expertise have established laboratories for the study of human cognition and behavior. A similar increase in number and scientific impact has occurred in regard to research institutes devoted to cognitive science, computer science, and multimedia applications. The newer institutions operate on long-term projects, and are often sponsored by corporations rather than individuals. Consequently, they tend to outperform university departments of psychology in attracting funds for more spacious laboratories with costly equipment such as high-resolution magnetic resonance imaging and high technology environments.

3.3 Wilhelm Wundt (1832–1920)

Wundt is commonly regarded as the founding father of Psychology, which established itself as a science around the beginning of the twentieth century. In 1879, Wundt founded the first psychological laboratory of the world in Leipzig, Germany, where he mainly studied sensations and feelings by employing experimental methods. This foundation also became influential outside Germany due to the many visits of foreigners—especially American students and scientists (see Hall, Granville Stanley (1844–1924)). Although Wundt often mocks at the methodology of Hegel's philosophy, he explicitly praises Hegel's achievement of ‘granting the right to exist to all ‘things in themselves,’ whether they are to count as metaphysical borderline concepts or as practical postulates’ (Wundt 1911, p. 736). Without this basis, it would have been impossible for Wundt to pursue Psychology as an empirical special science, because the soul would have been withdrawn from the applicability of methods borrowed from the natural sciences, as long as it were conceived of as an independent substance removable from the body (Descartes) or were postulated as such on practical grounds (Kant). Hegel, on the other hand, ‘has regarded the individual soul as the immediate relationship of the experiences of the soul, as a piece of that infinite reality of the world spirit, which still draws only on its very own actual reality to obtain all that it means’ (Wundt 1911, p. 736). So Wundt arrives at the conclusion that Hegel ‘had also declared the liberty of Psychology when it proclaimed for all that all mental coming into being—and, therefore, all happening in the soul as well—is actuality, is immediate experienced reality, and that essence and appearance of the Spirit are one and the same, and only mean something different in so far as we comprehend the essence as the relationship of the appearances which is correctly recognized’ (Wundt 1911, p. 737; own translations) (see for more Wundt, Wilhelm Maximilian (1832–1920)).

2 Introspection and Experiment

The turn to experimental methods of psychological investigation was closely linked to the controversial nature of introspection. Wilhelm Wundt, who played a major role in the launching of experimental psychology, believed that the psychological laboratory provided the only conditions under which reliable introspective data could be gathered (Danziger 1990). He accepted the distinction between inner perception and self-observation but, unlike his predecessors, totally rejected the latter. Instead, he advocated a control of the conditions of internal perception so as to approximate the conditions of external perception. This could be accomplished in the laboratory by such measures as the repetitive presentation of relatively simple stimuli and the requirement that reactions be immediate and automatic. However, adherence to these conditions would necessarily limit the scope of experimental psychology (and of valid introspection) to the investigation of ‘elementary’ psychological events, mainly in the areas of sensation and reaction times.

At the beginning of the twentieth century these restrictions were rejected by a new generation of experimental psychologists who greatly extended the scope of experimental introspection so as to enable them to investigate more complex psychological processes like thinking and problem solving. The reliability of results was now thought to depend on the adoption of certain attitudes while introspecting. But there was no unanimity about the nature of these attitudes. E. B. Titchener (see Structuralism, History of Structuralism), a major exponent of experimental introspectionism, demanded that introspective descriptions should be in terms of simple, irreducible, units and should abstract from any meaning the stimulus might have. In Europe, members of the Wurzburg School (see Humphrey 1951) emphasized the importance of clearing one's mind of preconceptions while introspecting. (Titchener's requirements were prime examples of such preconceptions). Later, the Gestalt psychologists extended this phenomenal approach by insisting that perceptions should be described exactly as they appear in daily life, i.e., in terms of interrelated, meaningful, patterns.

The investigations of the Wurzburg School raised a new kind of question: what is the relationship between the conscious experience of the introspector and the verbal report he or she makes of this experience? In the empiricist tradition it had always been assumed that the relationship is one of description, not different in principle from a description of objects experienced as located outside oneself. However, it now appeared that some of the verbal reports in introspection experiments could not be regarded as descriptions of inner states, they were much more like expressions of these states, e.g., when someone reports feeling: ‘Oh no, not that again!’ The German term for this is Kundgabe, which has connotations of broadcasting and proclaiming. This distinction pointed towards recognition of the communicative features of introspective reports. It also suggested that the result of treating introspective reports purely as descriptions of mental events was likely to be a misleadingly intellectualistic account of such events.

Background

Historically, psychology was considered academically as a component of philosophy until the late 19th century; a separation arose through the application of the scientific empirical method. The scientific empirical method replaced philosophical analysis as the primary method for approaching problems and added an additional source of information linked to the hermeneutic (interpretive) method in order to gain insight. Wilhelm Wundt established the first psychological laboratory in Leipzig in 1875; his influence was widespread initially in Germany, but this spread quickly to Britain and the United States, where psychological laboratories were established along the lines of Wundt's model in Leipzig. A student of Wundt's, Lightner Witmer, coined the term “clinical psychology,” which he defined in 1895 as follows: “While the term ‘clinical’ has been borrowed from medicine, clinical psychology is not a medical psychology. I have borrowed the word ‘clinical’ from medicine, because it is the best term I can find to indicate the character of the method, which I deem necessary for this work.…The term ‘clinical’ implies a method, and not a locality. Clinical psychology likewise is a protest against a psychology that derives psychological and pedagogical principles from philosophical speculations and against a psychology that applies the results of laboratory experimentation directly to children in the school room.”

Strongly under Wundt's influence, Witmer founded the first psychology clinic in Philadelphia in 1896 and applied the scientific method and knowledge of psychological principles to a range of psychological problems, particularly developmental disorders. The hermeneutic approach has been revived in the emergence of psychoanalysis—less, however, in its philosophical tradition, but more in terms of its meaningfulness for inference in clinical practice. Since the beginning of the 20th century, clinical psychology has grown considerably in theoretical scope and application, and as a consequence different types of measurement have evolved.

1 Historical Development

Transformation of the earth's surfaces by human beings has a long history. A primary aim is to create protection against threats to survival. In the 1960s the scientific study of the psychological effects of the humanmade environment began, largely motivated by a concern for the deterioration of human environments (e.g., Proshansky et al. 1970). A sensible early approach was to compare psychological effects of the humanmade environment with those of the natural environment in which the human species evolved (see Natural Environmental Psychology).

Research strategies in environmental psychology were first outlined by Craik (1968), based on the dominant strategy in personality assessment. Measurement issues were naturally at the forefront in the early research in environmental psychology. In particular, it was necessary for progress that methods were developed to assess physical settings outside the psychological laboratory as well as to assess how people react to such settings.

Important substantive research problems were originally defined by design professionals whose training made them sensitive to many subtle effects of the designed environment on human behavior. They used this knowledge in designing environments. However, in the face of criticism they became concerned about the scientific basis of their work. Social scientists observed a decline in the quality of urban life. To physiological psychologists this opened new meaningful research problems of how health and well-being are related to the physical environment. Cognitive psychologists concerned about the ecological validity of their research discovered in environmental psychology the possibility for investigating the acquisition, representation, and use of everyday knowledge (of the physical environment). Social psychologists saw in environmental psychology a way out of the laboratory to do meaningful research in the real world. Since the new focus on the physical environment did not stop them from analyzing the social environment, they offered influential conceptualizations in which the physical environment is presupposed to interact with the social environment in shaping human behavior.

The history of environmental psychology as well as its current status is documented in a series of comprehensive reviews published in Annual Review of Psychology, see, for example, Sundstrom et al. (1996). In 1987 the Handbook of Environmental Psychology was published under the editorship of Daniel Stokols and Irwin Altman. Following this benchmark publication several edited series of books have appeared with reviews of research in different subfields (e.g., Zube et al. 1987–97). Current research is primarily disseminated in three journals with slightly different emphases: Journal of Environmental Psychology, edited by David Canter, represents the psychological perspective; Environment and Behavior, edited by Robert Bechtel, covers the broader interdisciplinary field of environment–behavior research; and Journal of Architectural and Planning Research, edited by Andrew Seidel, is primarily an outlet for architectural and environmental design research. Several textbooks have also been written. The most comprehensive of these (Gifford 1997) cites approximately 5,000 studies.

1.1 Experimentation in Nineteenth-century Psychophysics

Psychological experimentation began as an endeavor of mid-nineteenth-century gentlemen-scholars to discover the given design of human nature. The word ‘experiment’ could refer to all kinds of research other than naturalistic observation. Experimentation involved manipulating human sensation and perception within artificial situations. An important founder of psychological experimentation was the German scholar Gustav Fechner, who during the years 1845 to 1849 lifted his arms with a weight in each hand over 67,000 times. After each lifting, Fechner meticulously recorded whether he had been able to distinguish the heavier weight from the lighter. In this way he established the ‘just noticeable difference’ or ‘threshold of perception’ as well as the mathematical relationship between the weights as measured and the weights as perceived.

In Fechner's time, the claim to measure anything as subjective as human sensation was novel and impressive. In the second half of the nineteenth century, innumerable ‘threshold experiments’ were conducted in biology, physiology, and particularly the newly established psychological laboratories at European and American universities. Countless extra weights were lifted, and Fechner's methods of ‘psychophysical’ experimentation were employed for testing other senses as well. A popular variation was touching the skin with two pins at specific distances and trying to establish the minimum distance that can still be perceived (see Fig. 1). The different sensitivities of foreheads, chins, shoulders, arms, fingers, hips, bellies, legs, knees, and ankles were discussed. Neophytes would complain about sensitive and scaly skins and apologetically argue that some 6,000 pricks should be enough to draw a conclusion (Dehue 1997).

Like Fechner, the first psychophysical researchers acted as their own experimental subjects. Soon, however, the idea arose that the stimuli should be applied in random order, and that random control trials were needed. Researchers in Germany and subsequently the USA argued that the perception of distances might be biased by expectations on the next distance to come. Such expectations might be induced by awareness of the actual distances in previous trials or inadvertent regularities in previous series of trials. Moreover, it was argued, the sheer knowledge that there are always two pins might arouse the idea of perceiving a distance even if the actual distance is below the threshold of perception. For these reasons, it was decided that it takes two to experiment. Assistants were employed to apply the stimuli in random order as well as randomly carry out control trials in which the skin was touched at one point only without knowledge of the ‘observers’ (later on the individuals providing the stimuli would be called the ‘experimenters’ and the observers became the ‘subjects,’ see Danziger 1990 on the social meaning of such terminological changes). These were the first experiments employing randomization as a methodological means. In the 1880s, the American scholars Charles S. Peirce and Joseph Jastrow, moreover, introduced the first artificial randomizers. Distrusting the assistants' ability to establish truly random orders, they used playing cards or dice (for a more extensive discussion and references, see Dehue 1997).

If the stimuli are indicated as ‘S,’ the responses as ‘R,’ and the randomly applied control trials (in which the actual double prick was withheld) as ‘noS,’ then the design of these experiments was something like S-R-noS-R-S-R-S-R-noS-R-S-R-noS-R-S-R-S-R (etc.). In later educational experimentation, the randomly inserted control trials (noS) were no longer conducted with the same subjects as the experimental trials (S) but with randomly composed control groups. This change implied the constitution of the random group design. In order to explain why that happened, some extra information should first be given on the methods of early psychophysics as well as social changes taking place outside the laboratories.

3 Wundt and the Genesis of the Discipline of Modern Psychology

Wundt made fundamental contributions to the genesis of the discipline of modern psychology in the nineteenth and twentieth centuries, in Germany and beyond. This genesis may be described generally in terms of six phases and their corresponding developmental features.

First, Wundt had a lasting impact on the development of the subject matter and methods of empirical psychology since the beginning of the nineteenth century with his ‘individual psychology.’ This is also true to a certain extent for his ‘ethnopsychology’, if historically developed products of mind are regarded as historical empirical experience.

Second, Wundt was influential in institutionalization, that is, founding institutes for experimental psychology and anchoring them in the university system, as well as other forms of institutionalization, such as the founding of scholarly journals and scholarly societies. Active in scientific policy making, Wundt made a definitive contribution to institutionalization by founding the world's first psychological laboratory, the Institute for Experimental Psychology at the University of Leipzig in 1879. He also founded one of the first experimental journals in psychology, Philosophical Studies in 1881.

Third, Wundt can be said to have contributed to the temporary division into major schools during the period between about1890 and 1940, inasmuch as his institute became a model for psychological institutes in many countries. But he did not found an actual school in the strict sense of the Berlin school of Gestalt psychology, the Würzburg school of cognitive psychology, or the Vienna school of psychoanalysis.

The fourth phase is the development of applied psychology, that is, through the inclusion and development of fields of praxis outside the universities and higher education after about 1890. Wundt had an ambivalent, rather negative relationship to the development of applied psychology. In his opinion, psychology should attempt a transition to practical applications only after its foundation has been systematically constructed (Wundt 1913).

Fifth, with his twofold psychology and with numerous students from many countries, Wundt made a definitive contribution to the development of a pluralistic system of psychology and to the gradual integration of the major schools after about 1930.

The final phase is professionalization, that is, the establishment, social anchoring, and state certification of standards for academically educated psychologists active outside of the university system around the time of World War I. With his early work in developing a curriculum for the education and training of psychologists, Wundt contributed indirectly to professionalization. This curriculum, with further contributions from other psychologists, was adopted in 1941 in the form of the first state diploma examination regulations in Germany.

The genesis of the discipline described above was initially, in the nineteenth century, determined primarily by experimental psychology. This constituted the first phase of methodological development in which experimental methods, the technical apparatus and the mathematics of experimental physics and of experimental physiology were transferred to psychology. Wundt's ‘individual psychology’ is an expression of this development. It thus becomes understandable why many of the ‘pioneers’ of modern psychology, Wundt's contemporaries in nineteenth-century Germany, were trained as experimental physicists or experimental physiologists. They include Ernst Heinrich Weber (1795–1878), anatomist and physiologist, Gustav Theodor Fechner (1801–87), doctor and physicist, and Hermann von Helmholtz (1821–94), physiologist and physicist.

During the second half of the nineteenth century a second phase of methodological development began. More or less standardized nonexperimental methods were added step by step to the experimental procedures. These methods were initially analytical documentary procedures that Wundt called methods of ‘comparison’ within his ‘ethnopsychology.’ Later they also included the preexperimental empirical methods based on the paradigms of assessment, achievement, arrangement, and interpretation. These methods contributed significantly to the development of psychodiagnostic procedures. Both groups of nonexperimental procedures today constitute elements of ‘historiographic’ and ‘quasi-experimental’ methodology in psychology. Wundt's work and its influence may be categorized within these two phases of nineteenth-century methodological development: his experimental ‘individual psychology’ falls within the first phase and his nonexperimental ‘ethnopsychology’ within the second.

1 Historical Developments

The development of the two aspects of the study of ‘brain, mind and behavior’ is best viewed historically. As noted above ‘behavioral neuroscience,’ the subject of this article, is the modern equivalent of ‘physiological psychology.’ Since Wilhem Wundt, the founder of the modern field of psychology in the 1870s and himself a physiologist, titled his epoch making text Grundzüge der Physiologische Psychologie (1874), we begin with his era. Wundt insisted on the experimental approach to all questions of psychology: the challenge was to find experimental methods to understand psychological processes. The most appropriate methods, e.g., measures of brain activity, did not of course exist in his day. Indeed, the only methods available were simple measurements of behavior like reaction time, and verbal descriptions of experience by introspection, both of which were used in Wundt's laboratory.

Wundt's career illustrates well the roots of the developing field of physiological psychology. After a year of study at Heidelberg in basic medical sciences, he moved to Berlin and worked for two years with Johannes Müller, a founder of modern, experimental physiology. Müller, incidentally, was a vitalist and believed that it would never be possible to measure the speed of the nerve impulse; his own student Helmoltz proved him wrong. Wundt then took his doctorate in medicine and was appointed Dozent in physiology at Heidelberg. Helmholtz then joined the same institute and they were colleagues, but not collaborators, for a period of 13 years. Wundt later moved to Leipzig and established the first formal psychological laboratory, in 1879.

Wundt's text and research at Leipzig represented a brilliant experimental physiologist grappling with problems of the mind and mental events, applying the experimental methods of science as best he could. In fact, the bulk of the research done in the Leipzig laboratory was on sensation and perception, and on reaction time.

Another laboratory of physiological psychology was founded at about the same time, that of William James. James went to Harvard and Harvard Medical School and studied with the great naturalist, Louis Agassiz. James was then, after a year of study abroad, appointed an instructor in physiology at Harvard College in 1872. He actually established an informal physiological psychology laboratory there in 1877 and taught a graduate course on the relations between physiology and psychology.

In sum, the two founders of modern psychology, Wundt in Germany and James in America, were both physiologists by training. More than a third of William James' extraordinary and influential text, Principles of Psychology (1890), was devoted to the nervous system. However, this does not necessarily mean that Wundt and James attempted to reduce psychology to physiology; rather they proposed that the subject matter of psychology should be studied scientifically, as in physiology. This view could equally apply to behavioral and cognitive neuroscience as it exists today.

There were powerful intellectual pressures moving bright young physiologically inclined psychologists at the turn of the century. The theory of evolution was a major force. The field of physiology, in particular neurophysiology, in the work of Sir Charles Sherrington and then Lord Adrian, together with clinical neurology and neuroanatomy, were vigorous and exciting fields at the beginning of the twentieth century.

The development of instrumentation was still another very important factor. The human EEG was rediscovered in 1929 (Berger) and the method applied to animal research in the 1930s. At the turn of the century the major experimental techniques for the study of brain function were ablation and electrical stimulation. Neuroanatomy was in its descriptive phase; the monumental work of Ramon y Cajal was published over a period of several decades beginning near the end of the nineteenth century. Neurochemistry was in its purely descriptive phase.

Merely because techniques and basic knowledge were limited does not mean that the field was quiescent. On the contrary, there was ferment over a number of basic issues ranging from the mind-brain problem to localization of function and the nature of neuronal interactions. Add to this the ferment developing in psychology as John Watson took on the older establishment and behaviorism began to dominate. This is the background from which modern physiological psychology developed.

7 Social Philosophy

Skinner's social philosophy was based in a deep confidence that only science would help us in solving the problems we are facing in our modern societies. What is needed is a science of behavior, which in fact is now available, he thought, and could be applied if only we would be ready to abandon traditional views of human nature. He first expressed his ideas in the novel Walden Two (1948). Written two years after the end of the World War Two, the book describes a utopian community run after the principles derived from the psychological laboratory. It is by no means a totalitarian society, as some critics have claimed. Looked at retrospectively, it is surprisingly premonitory of social issues that are still largely unsolved half a century later. For instance, working schedules at Walden Two have been arranged so that all tasks needed for production of goods and good functioning of the community are distributed among members according to a credit system which results in an average amount of 24 hours per week, avoiding unemployment, abolishing any social discrimination between manual and intellectual work, and leaving many free hours for leisure activities such as sports, arts, and scientific research. Emphasis is put on active practice rather than passive watching, on co-operation rather than competition. The community is not isolated culturally: cultural products from outside such as books or records are of course welcome, but radio programs are filtered to eliminate publicity. Education is active; the school building symbolically has no door separating it from the life and work community; there are no age classes, no humiliating ranking; all learn at their own rhythm, in whatever orientation they feel appropriate, throughout their life time. Women enjoy complete equality with men. Waste of natural resources is avoided. Special charges in the management of the community are strictly limited in time, eliminating any risk of political career.

Similar themes, plus the frightening concerns with pollution, violence, uncontrolled population growth, nuclear weapons, and the like, are further elaborated in the essay Beyond Freedom and Dignity (1971) and a number of later articles. In an alarming tone, Skinner points to what he feels is the core of our inability to deal with these issues, that is our obstinacy in keeping a conception of human nature which scientific inquiry shows us to be wrong, and which bar any solution to the problems we are confronted with. We still stick to a view of humans as being the center of the universe, free and autonomous, dominating nature, while we are but one among many elements of nature. As a species, we are the product of biological evolution; as cultural groups, the result of our history; and as individuals the outcome of our interactions with the environment. Because we fail to admit this dependency, and draw the consequences of it, we might put in danger our own future. Freedom, autonomy, and merit are no absolute values: they were forged throughout history, and more often than not they are used to disguise insidious controls, the mechanisms of which should be elucidated if we want to develop counter-controls eventually allowing for the survival of our species.

Skinner viewed these various facets of his work as closely related, making for a highly consistent theory of human behavior, in which the critical analysis of social processes in modern society was deeply rooted in the experimental analysis of the behavior of animal subjects in the laboratory. So global an ambition has been criticised, and clearly various aspects of his contribution did not have the same fate. If the operant technique is now a widely used procedure to many purposes in experimental research in psychology and related fields, if his early attempts to build teaching machines appear now as ancestors of computer assisted learning and teaching, if a number of principles of contingencies analysis are now currently put in practice in behavior therapies, radical behaviorism has been seriously questioned and even shaken by the rise of the cognitivist approach in psychology, while Skinner's social philosophy has been attacked from different fronts both on ideological and scientific grounds.

As most great theory builders of the twentieth century in psychology, from Sigmund Freud and Watson to Jean Piaget, Skinner may be blamed for having reduced the explanation of human nature to a very limited set of concepts and findings, namely those he had forged and observed in his own restricted field of research and reflection, ignoring even other concepts and facts in neighboring fields of psychology, leaving alone of other sciences. It is clear that Skinner has made no attempt at integrating, for example, contributions of developmental or of social psychology, nor those of sociology, cultural anthropology, or linguistics. Such neglects might have been deliberate, legitimated by the will to concentrate on what were, in Skinner's mind, essential points left out by other branches of psychology or other sciences dealing with human societies. However, they might appear as sectarianism to those who favor an integrative and plurisdisciplinary approach to the complex objects of human sciences. It cannot be decided whether his influence would have been larger or smaller had he adopted a less exclusive stand.